Production of quinone and hydroquinone



Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE PRODUCTION OFQUINONE AND HYDRO- QUINONE No Drawing. ApplicationDecember 12, 1934, Se-

rial N0. 757,236. In

9 Claims.

This invention relates to the production of quinone (p-benzoquinone) andhydroquinone (1.4 dihydroxy-benzene) It is known that when benzene,agitated with a neutral or acid electrolyte, for example sulphuric acidwhich is maintained cool, is electrolyzed between electrodes which areunattacked by the electrolyte e. g. lead electrodes, the benzene ispartially converted into quinone at the anode.

Since quinone is soluble in water and in aqueous solutions and iscathodically reduced to hydroquinone it has been usual to carry out theoxidation in a cell divided into two, by a porous diaphragm so as toavoid the wastage of current by 15 the passage of quinone andhydroquinone between the electrodes.

An object of this invention is to provide an improved process for theproduction of quinone by anodic oxidation.

A further object of this invention isto provide an improved process forthe production of hydroquinone from the dilute solution of quinone inbenzene obtained by the anodic oxidation process of the invention.

It has been found according to this invention that a high yield ofquinone can be obtained without the use of a diaphragm, thedisadvantages of which are well known.

According to the process of this invention for 30 the production ofquinone, benzene is passed through or stirred with an electrolytepreferably consisting of dilute sulphuric acid or a mixture of sulphuricacid and a soluble sulphate such as sodium sulphate, and subjected toelectrolysis in 35 an electrolytic cell in which an active and stableanode and an inactive cathode are disposed preferably close to eachother, the concentration of quinone in the cell being kept low by itscontinuous or frequent removal.

The electrolyte is preferably dilute sulphuric acid and it maybe of anyconcentration up to 20% of H2804. Too low an acid concentration resultsin an electrolyte of low electrical conductivity, while too high aconcentration results in the destruction of quinone. An acidconcentration of 10% of H2804 has been found to be satisfactory.

The addition to the electrolyte 0.? acetic acid or other organic acidsor salts of o ganic acids has been proposed for the purpose ofincreasing the solubility of the benzene in the electrolyte.

We have tried these additions but have found that they do not increasethe eificiency of the process.

The temperature of the electrolyte should not Great Britain Decemberexceed 25 C. and ordinarilya temperature of 20 C. is a suitabletemperature at which to operate. Temperatures higher than 25 C. do notgive a good yield. Although temperatures lower than 20 C. may be usedthey do not possess any advantage to compensate for the extra cost ofcooling and the higher cell voltage which lower temperatures entail. Thetemperature may be maintained within the required limits by the passageof cold water through a coil serving as cathode as described hereafter.

The anode may be of lead or an alloy of lead. Its surface becomes coatedwith lead peroxide when current is passed and the condition of thiscoating of peroxide influences the efliciency of the formation ofquinone. It has been found that the peroxide coating should not be toothick and should not be of such a nature as to scale off and that a hardlead alloy for example an alloy of lead with antimony or an alloy oflead with bismuth forms a more stable peroxide surface than pure lead.

The anode surface may be rendered active and stable by the passage of analternating current or an alternating current superimposed on a directcurrent through the cell in the absence of the cathode and before theintroduction of the benzene, or in another cell.

Thus, for example, the electrode to be used together with a similarlyshaped piece of lead may be disposed in an electrolytic cell, theelectrolyte being dilute sulphuric acid. Electric current is passedthrough the cell, the direction of the current being frequently reversedby means of a suitable switch. The last change of currentis efi'ected sothat a coating of lead peroxide is formed on the electrode to be used.The anodic current density may vary between fairly wide limits but ithas been found that densities of between 5 and amperes per squaredecimetre give the best results.

The cathode may be of any metal that is unattacked by the electrolytebut metals such as copper which promote the reduction of quinone shouldbe avoided. Lead is a satisfactory metal to use as the cathode. Thecathcathode,

for cooling is passed through the cathode which may conveniently consistof a lead coil.

High cathodic current density is accompanied by low reduction of quinoneand the cathodic current density should therefore be higher, preferablyat least 50% higher, than the anodic current density. In other words thearea of the oathode should be less than that of the anode.

The electrolyte is preferably covered with a layer of benzene which isstirred into the electrolyte by means of a suitable agitator. Theagitation should be sufficient to ensure constant circulation of benzenearound the whole of the anode, but it should preferably be not soviolent as to cause fine emulsification of the benzene with consequentslow separation of the benzene and electrolyte. Fresh benzene is addedcontinuously or at intervals and an equivalent volume of benzene-quinonesolution is withdrawn from the cell for example by overflow. The feedand overflow should be adjusted to prevent the concentration of quinonein the benzene from rising above 15 grams per litre. This prevents thequinone concentration in the electrolyte from rising above about twograms per litre.

Some benzene is lost from the cell, being carried away by the stream ofmixed gases evolved, this loss may be partly avoided by the use of asuitable condenser which may be maintained at a sufliciently lowtemperature to freeze out the benzene. The stream of mixed gases mayalternatively be made to pass through a known absorbent and afterwardsrecovered therefrom, or a combination of cooling and an absorbent may beused.

The benzene which is oxidized to quinone may contain dissolved thereinphenol and/or aniline which are easily oxidized to quinone during thecourse of the reaction. If desired regulated quantitles of aniline andphenol may be added to the benzene during the reaction.

If quinone is required as a final product it may be separated from thebenzene by known methods, for example by distilling off some of thebenzene and crystallizing the quinone. As hereinbefore indicated,however, the quinone may be converted into hydroquinone which as isknown is extensively used for photographic purposes.

Several methods have been proposed for the production of hydroquinone.For example it has been proposed that a benzene solution of quinoneshould be added to the cathode compartment of a divided electrolyticcell, or that it should be agitated with water and sulphur dioxide.

In both these proposed processes quinhydrone is first formed, and itslow solubility makes its further reduction to hydroquinone slow anddifiicult. Also it tends to collect at the interface of the liquidphases and to cause stable emulsification of the benzene in the water.

According to the process of this invention for the production ofhydroquinone the benzene solution of quinone produced in the mannerhereinbefore described is subjected to reduction at about the boilingpoint of benzene and under such conditions that the benzene isimmediately distilled 011 and the hydroquinone dissolved in water.

The reduction may be carried out by means of iron and acid,sulphurdioxide or other known reducing agents. Quinone is rapidlydestroyed at these temperatures so the conditions must be such thatreduction is rapid and complete and the benzene solution must be addedgradually to the reduction vessel.

Thus a solution of quinone in benzene run from the cell may be treatedwith iron borings and water containing a little sulphuric or othersuitable acid in a heat jacketed or otherwise heated vessel.

The vessel with the contents are kept at a temperature of about C., thebenzene solution is run in slowly, the benzene distills over and iscondensed, and the quinone is entirely reduced to hydroquinone whichremains in the vessel in aqueous solution. The acid liquors from thevessel are occasionally withdrawn and the hydroquinone recoveredtherefrom. Preferably the hot saturated liquors are drawn oil, filteredhot and cooled when hydroquinone crystallizes out. The acid motherliquor is returned to the reduction vessel. The hydroquinone may berecrystallized from water or other solvent.

Alternatively the aforesaid quinone-benzene solution may be run into astill containing water into which sulphur dioxide is simultaneously ledin amount equivalent to that of the quinone to be reduced. The benzenedistils off and is condensed and the hydroquinone formed remains behindin solution in the water together with the sulphuric acid formed in thereaction. At intervals the aqueous solution is withdrawn the acidremoved by means of calcium carbonate, lime or barium carbonate orhydroxide and the hydroquinone obtained by evaporation. By using an ironfree distillation vessel the hydroquinone may in this way be obtainedabsolutely free of iron.

The following example illustrates how the process of the invention maybe carried into effect:

The cell employed is capable of operating at 1000 amper'es. The anodeconsists of an alloy of lead containing 10% of antimony made in tubularform with leads attached to carry the current. The whole of the tubularsheet is freely perforated so that under agitation the benzene passesfreely through it. This electrode has a total surface area of 125 squaredecimetres, the diameter being about 40 centimetres. The cathodeconsists of a lead pipe of outside diameter 2.5 centimetres and 1100centimetres long made in the form of a coil of 44 centimetres internaldiameter suitably stiffened. The cell container of glazed earthenware orother suitable inert material has a capacity of about 100 litres and hasa bottom outlet and an overflow pipe near its upper edge. A lid ofsuitable form to make a tight joint is provided and the cell is chargedwith litres of sulphuric acid containing about grams of H2804 per litre.Current is then passed until the anode which has been activated iscoated with lead peroxide, after which 15 litres of benzene are added.The cell agitator is introduced through a central hole in the lid andoperates inside the anode cylinder. The agitator is of aluminium havingsix blades which when rotated carries the benzene downwards through theelectrolyte but does not give fine emulsification. The electrolytecovers the whole of the effective electrode surface and the top blade ofthe agitator is just immersed in the electrolyte. The addition of 15litres of benzene allows the passage of about 1000 ampere hours beforethe concentration of quinone in the benzene attains a value of about 10grams per litre. At this point the benzene feed to the cell is startedat the rate of about 15 litres per hour. Cooling water is passed throughthe cathode coil in sufficient volume to maintain the temperature of theelectrolyte at 20 C. The benzene overflow level is fixed so that 15litres of benzene remain in the cell, the overflow being led to a stillfor the separation of p-benzoand fitted with a suitable condenser, thetemperature is adjusted so that the benzene is immediately distilledover. The vessel is charged with 1.5 kilograms of iron borings togetherwith 4 litres of water and 1 to 2 grams of sulphuric or acetic acid. Thecell operating at 1000 amperes maintains an overflow of about 15 litresof benzene-quinone solution which continuously passes to the reductionvessel. The benzene beingdistilled, condensed and separated from anywater which may distil over, is returned to the feed vessel of the cell.The quinone is completely and efliciently reduced to hydroquinone whichdissolves and accumulates in the acid water contained in the reductionvessel. This vessel is maintained at a temperature of about C. and thereduction carried on until the solution of hydroquinone is. saturated ata temperature of about 60 C. when it isrun off through a filter toremove iron oxide. The filtrate is allowed to cool and the crystallizedhydroquinone separated by filtration. The acid mother liquor is returnedto the reduction still together with any water separated from thebenzene distillate.

The cell is kept in'continuous operation maintaining theconditions setforth until the electrolyte becomes fouled with oxidation products ofbenzene which dissolve in the electrolyte which is then discarded. Thecell also at times needs cleaning owing to the separation of matterwhich 'is insoluble in both the electrolyte and the henzene but thiswill not occur at more frequent intervals than after a continuous run of24 hours.

The cell under the conditions stated produces crystallized from waterafter being treated with a small quantity of decolourizing carbon itgives a product which has the theoretical melting point. If desired thehydroquinone may be extracted with ether or other organic solvent toobtain a pure product.

The process described in the foregoing example may be efiected in thepresence of aniline and/or phenol but it should be conducted in such away that the concentration of aniline does not exceed 5 grams per litreand the concentration of phenol does not exceed 1 gram per litre in theelectrolyte.

What we claim is:-'-

1. A process for the production of quinone comprising subjecting amaterial selected from the group consisting of lead and alloys of leadto the passage of an alternating current in an acid electrolyte to forman active and stable anode, electrolyzing a mixture containing benzeneand an electrolyte by means of direct current passed between said activeand stable anode and an inactive cathode without the use of a diaphragm,removing resultant quinone as a solution in benzene and supplying morebenzene to the cell, and so adjusting such removal and supply as to keepthe quinone concentration of said solution relatively low.

2. A process for the production of quinone comprising subjecting amaterial selected from the group consisting of lead and alloys of leadto the passage of an alternating current superimposed on a directcurrent in an acid electrolyte to form an active and stable anode,electrolyzing a mixture containing benzene and an electrolyte by meansof direct current passed between said active and stable anode and aninactive cathode without the use of a diaphragm, removing resultantquinone as a solution in benzene and supplying more benzene to the cell,and so adjusting such removal and supply as to keep the quinoneconcentration of said solution relatively low.

3. A process for the production of quinone comprising subjecting amaterial selected from the group consisting of lead and alloys of lead'to the passage of an alternating current in an acid electrolyte to forman active and stable anode, electrolyzing a mixture containing benzeneand an electrolyte by means of direct current passed between said activeand stable anode and an inactive cathode without the use of a diaphragm,removing resultant quinone as a solution in benzene and supplying morebenzene to the cell, and so adjusting such removal and supply as to keepthe quinone concentration of said solution from exceeding 15 grams perliter.

4. A process for the production of quinone comprising subjecting amaterial selected from 1 the group consisting of lead and alloys of leadto the passage of an alternating current in an acid electrolyte to forman. active and stable anode, electrolyzing a mixture containing benzeneand a solution containing sulphuric acid by means of direct currentpassed between said active and stable anode and an inactive cathodewithout the use of a diaphragm, removing resultant quinone as a solutionin benzene and supplying more benzene to the cell, and so adjusting suchremoval and supply as to keep the quinone concentration of said solutionrelatively low.

5. A process for the production of quinone comprising subjecting amaterial selected from the group consisting of lead and alloys of leadto the passage of an alternating current in an acid electrolyte to forman active and stable anode, electrolyzing a mixture containing benzeneand a solution containing sulphuric acid and a soluble sulphate bymeansof direct current "zene and an electrolyte by means of direct currentpassed between said active and stable anode and an inactive cathode.said anode and said cathode being disposed close to one another and withno intervening diaphragm, removing resultant quinone as a solution inbenzene and supplying more benzene to the cell, and so adjusting suchremoval and supply as to keep the quinone concentration of said solutionrelatively low.

'7. A process for the production of quinone comprising subjecting a hardlead alloy to the passage of an alternating current in an acidelectrolyte to form an active and stable anode, electrolyzing a mixturecontaining benzene and an electrolyte by means of direct current passedbetween said active and stable anode and an inactive cathode without theuse of a diaphragm, removing resultant quinone as a solution in benzeneand supplying more benzene to the cell, and so adjusting such removaland supply as to keep the quinone concentration of said solutionrelatively low.

8. A process for the production of quinone comprising subjecting analloy of lead and a material selected from the group consisting of antimony and bismuth to the passage of an alternating current in an acidelectrolyte to form an active and stable anode, electrolyzing a mixturecontaining benzene and an electrolyte by means of direct current passedbetween said active and stable anode and an inactive cathode without theuse of a diaphragm, removing resultant quinone as a solution in benzeneand supplying more benzene to the cell, and so adjusting such removaland supply as to keep the quinone concentration of said solutionrelatively low.

9. A process for the production of quinone comprising subjecting amaterial selected from the group consisting of lead and alloys of leadto the passage of an alternating current in an acid electrolyte to forman active and stable anode, electrolyzing a mixture containing benzene,an electrolyte and at least one substance selected from the groupconsisting of phenol and aniline by means of direct current passedbetween said active and stable anode and an inactive cathode without theuse of a diaphragm, removing resultant quinone as a solution in benzeneand supplying more benzene to the cell, and so adjusting such removaland supply as to keep the quinone concentration of said solutionrelatively low.

HERBERT PALFREEMAN. NORMAN VICTOR SYDNEY KNIBBS.

